1. Field of Invention
The present invention relates to an electric motor, and more particularly to a DC motor assembly with step adjusting control arrangement especially for a container, which is adapted to adjustably control the rotational speed of the output shaft of the DC motor in a stepping manner.
2. Description of Related Arts
A conventional DC motor generally comprises an output shaft for generating a rotatable power. In order to control the rotational speed of the output shaft, the DC motor has two terminals being electrically connected with a power source. When the output voltage of the power source is increased, the rotational speed of the output shaft is correspondingly increased. Likewise, when the output voltage of the power source is reduced, the rotational speed of the output shaft is correspondingly decreased. On the other hand, a load at the output shaft will also change the rotatable power thereof. When the load is increased, the rotational speed of the output shaft is correspondingly decreased. When the load is reduced, the rotational speed of the output shaft is correspondingly increased. In order to provide a stable rotatable power of the output shaft, the DC motor further comprises a feedback control to control the rotational speed of the output shaft. Accordingly, when the rotational speed of the output shaft is determined below a predetermined threshold, the feedback control will send a feedback signal to the DC motor for increasing the output voltage so as to adjustably increase the rotational speed of the output shaft. In other words, the rotatable power generated from the DC motor will be selectively adjusted in responsive to the feedback signal in order to provide a stable rotational speed of the output shaft. However, the feedback control has a major drawback that the feedback control cannot control the angular phase shift of the output shaft that the output shaft can be stopped at a desired angular position and cannot adjust the step rotational speed of the output shaft. In addition, the domestic electrical appliance is cost ineffective when the domestic electrical appliance incorporates with the motor having the feedback control because the motor will substantially increase the manufacturing cost of the domestic electrical appliance.
Accordingly, the step motor, or named stepper motor, is an electric motor that can divide a full rotation into a large number of steps, wherein the output shaft can be controlled precisely at its angular position. However, the cost of the step motor is relatively high such that the step motor is cost ineffective when the domestic electrical appliance incorporates with the step motor. In other words, most of the domestic electrical appliance will only use the motor, especially the permanent magnet type DC motor.